1. Field of the Invention
The present invention relates to a document feeding apparatus having a document tray movable up and down.
2. Description of the Related Art
In recent years, an image reading apparatus has been widely used that is configured to convert image information of a document into digital data and outputs the resultant digital data to an image forming apparatus such as a printer or a storage device such as a computer connected to a network. Important specifications of such an image reading apparatus include a high capacity of reading a large number of documents at a high speed, and a short FCOT (First Copy Output Time), i.e., a capability of outputting a first copy in a short time after a copy start command is issued. Accordingly, there is a need for an increase in the maximum number of documents to be set at a time on a document tray of a document feeding apparatus. Thus, there is a need for an automatic document feeding apparatus having a document tray configured to be movable up and down by a lifter mechanism whereby documents can be properly handled regardless of whether a large or small number of sheets of documents are set on the document tray.
U.S. Pat. No. 6,091,927 discloses an automatic document feeding apparatus having a document tray with a lifter mechanism configured to be selectably operable in a first or second mode. In the first mode, the document tray is automatically raised in response to detecting setting of a document on the document tray. In the second mode, the document tray is raised in response to receiving a paper feed start signal.
Japanese Patent Laid-Open No. 09-166831 discloses an automatic document feeding apparatus having a document tray with a lifter mechanism configured to operate such that when feeding of documents is to be performed, the document tray is first raised and then feeding of documents is started. If a final document on the document tray has been fed, the document tray is lowered.
However, in the first mode disclosed in U.S. Pat. No. 6,091,927, the document tray is automatically raised immediately in response to detecting setting of documents on the document tray. In a case where a document stack including a large number of documents is set on the document tray by putting the document stack part by part, the document tray starts to rise in the middle of the operation of putting some part of the document stack. A user has to put remaining parts of documents on the document tray while the document tray is rising, and thus there is a possibility that the document tray reaches a paper feed position before all documents are set on the document tray. That is, there is a possibility that the user cannot set all documents on the document tray. If documents are set forcibly on the rising document tray, the documents are set in a space that is decreasing with rising of the document tray, and thus there is a possibility that the documents are not set properly. This leads to a possibility that documents are folded or a document feed error such as jamming can occur after feeding of documents is started.
In the second mode in U.S. Pat. No. 6,091,927 and also in the technique disclosed in Japanese Patent Laid-Open No. 09-166831, the document tray is raised to a paper feed position in response to inputting of a start command, and documents are sequentially moved to a document feed path. In this case there is substantially no possibility that a user sets documents incorrectly on the document tray. However, in a case where a small number of documents are set on the document tray, the document tray has to be raised a large distance until it reaches the paper feed position. The result of this is an increase in time spent before it becomes ready to start feeding documents.
In a technique disclosed in Japanese Patent Laid-Open No. 2004-166052, a document tray is raised when a start key or one of print condition setting keys disposed on an operation panel is pressed in a state in which documents are set on the document tray.
However, in the technique disclosed in Japanese Patent Laid-Open No. 2004-166052, if a user touches by mistake one of print condition setting keys during an operation of setting a large number of documents on the document tray, the document tray is raised against the intention of the user. In particular, in the case of an operation panel of a touch panel type, touching lightly can be detected as inputting of a command, and thus there is a large probability that an erroneous operation occurs.